Sliding compressor cylinder



Jan, 13, 1948 w. A. LEDWITH SLIDING COMPRESSOR CYLINDER 2 Sheets-Sheet 1 Filed July 6, 1945 INVENTOR 2M2 a M Jan. 13, 1948. w. A. LEDWITH SLIDING COMPRESSOR CYLINDER Filed July 6, 1945 2 Sheets-Sheet? INVENTO iflai 4 Patented Jan. 13, 1948 SLIDING COMPRESSOR GER Walter A. Ledwith, Manchester, Conn, assignor to United Aircraft Corporation, East Hartford, Conn, a corporation of Delaware Application July 6, 1945, Serial No. 603,494

7 Claims. (Cl. 230-56) The invention relates to free-piston units and particularly to a unit adapted to operate over a wide ranging of intake pressures.

In adapting a free-piston compressor for pumping fluids of various densities it is advantageous to be able to change the effective length of the compressor stroke without materially changing the overall length of the piston stroke since an excessive shortening of the stroke would prevent the engine ports from being properly uncovered by the pistons during the operation of the unit. A feature of this invention is the control of the effective length of stroke by axial adjustment of the compressor cylinder with respect to the piston stroke. Another feature is the provision of openings in the cylinder wall with means for axially shifting the position of the openings with respect to the piston stroke for changing the point at which the compression stroke begins.

The copending application of Kalitinsky, Serial No. 550,886, describes a control for free-piston units which involves the successive opening or closing of a number of rows of spill ports in the compressor cylinder, thereby varying the effective length of the compressor stroke, A feature of this invention is an alternative arrangement for accomplishing the same result by moving the compressor cylinder axially with respect to the piston. In this way, the ports are closed by the piston itself during its reciprocation. Thus, another feature of the invention is the elimination of the necessity for spill port closing bands and the mechanism for actuating them.

A feature is the increase in vent area in the compressor area to provide a sharper cut-ofl at the start of the effective part of the compression stroke.

Other objects and advantages will be apparent from the specification and claims, and from the accompanying drawings which illustrate an embodiment of the invention.

Fig. 1 is a sectional view through the freepiston unit.

Fig. 2 is a fragmentary sectional view showing the actuating means for the compressor cylinder.

Fig. 3 is a section on line 3-3 of Fig. 2.

The unit shown includes an engine cylinder Io having reciprocating pistons l2 and I4 to which compressor pistons I6 and I8 in cylinders 20 and 22 are integrally connected. Sleeves 24 and 26 attached to the compressor pistons complete the reciprocating piston assemblies. The sleeves in combination with stationary pistons 28 and 30 form air sprin cylinders.

The pistonassemblies are moved apart by the 2 burning of fuel injected into engine cylinder it through one or more nozzles, not shown. Air

compressed in the air spring cylinders on the power stroke returns the piston assemblies. The assemblies are always maintained at equal distances from the center of the engine cylinder by a linkage, not shown, of well known construction,

Intake manifold 32 which extends around the compressor and engine cylinders conducts air to intake valves 34 in the outer heads of the compressor cylinders. Air enters the Outer ends of the cylinders through these intake valves and leaves the cylinders through discharge valves 36, also mounted in the outer heads of the compressor cylinders. The air discharged through valves 36 passes into end scavenge chambers 38 and 40 which may be connected by a manifold, not shown, to a central scavenge chamber 42.

Compressed air from the scavenge chamber 42 enters engine ports 44 and 46 which are uncovered by pistons l2 and I4 at the end of the power stroke, thereby permitting air to be blown through the engine cylinder, Gas in the engine cylinder is discharged through exhaust ports 48 into exhaust manifold 50.

In adapting the unit to operate over a wide range of intake pressures each compressor cylinder 2D or 22 has its outer wall 52 or 54 provided with a row of ports 56 and 58, respectively, which permit the fiow of air into and out of the compressor cylinder. Each compressor wall 52 or 54 is cylindrical and is adapted to be guided for endwise movement by guides 60 and 62 in end caps 64 and 66, respectively, and at the inner ends by guides 68 and 10 which may also function to support the outer ends of the engine cylinder. The supports 68 and 10 may be located within the housing or manifold 32 by a number of radially spaced bosses 12.

The effective length of the stroke of the compressor pistons is changed by axially sliding the cylinder walls 52 and 54 away from the center of the engine cylinder for shortening the effective stroke and toward the center of the engine cylinder for lengthening the engine stroke. This may be done by any mechanism which may include brackets 14 and 16, Fig. 2, on the cylinder walls 52 and 54, respectively. Each cylinder wall, as shown in Fig. 3, may have a number of projecting brackets 14 or 16. each of which is engaged by a threaded rod 18 Fig. 2. By utilizing the number of threaded rods the cylinder may be slid axially uniformly, thereby preventing binding as the cyl inder is moved.

Each of the rods 18 has mounted thereon a gear 88 which meshes with a large diameter ring gear 82 extending around the compressor cylinder and supported against axial movement by a cap 84 which also supports one of the gears 80 and by other caps 86, Fig. 3, which support the other two gears. When any one of the gears 80 for either of the compressor cylinder walls is turned'it turns therewith the gear 82 and assures a corresponding rotation of the other gears 80 meshing with the same ring gear.

Both cylinder walls are moved simultaneously by an interconnecting driving mechanism which may include a rod 88 journaled in the spaced caps 84 and having gears 90 meshing with the corresponding gears 80 of the opposite cylinder walls. The rod 88 may be turned manually or by any driving mechanism. It will be apparent that turning of the rod 88 counterclockwise, as seen from the right of Fig. 2, will turn the rods '18 for the right hand compressor counterclockwise, thereby, if the threads on the rod 18 are right hand threads, moving the compressor cylinder inward toward the center of the unit. To obtain a correspondingmovement of-the left hand compressor cylinder wall 52 inward toward the center of the engine the rods 18 for this compressor cylinder will obviously have the threads opposite to the threads for the right hand cylinder, or in this case the threads for the left hand cylinder will be left hand threads.

Since the effective stroke of the compressor pistons is that part of the stroke between the outer edges of the ports 56 and 58 and the outer end of the piston stroke, it is apparent that the stroke is lengthened by moving the compressor wall inward toward th center of the engine or is shortened by moving the compressor walls outwardly away from the center of the engine,

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.

I claim:

1. In a free-piston unit, an engine cylinder, and

a free-piston therein, a compressor cylinder and piston, the compressor piston being connected to and moving with the engine piston, said compressor cylinder having a compressor head and a cylindrical wall, said cylindrical wall having at least one port therein for the escape of gas within said compressor, and means for shifting the position of said port axially with respect to said compressor head to adjust said port axially relative the normal position of the piston stroke.

2. In a free-piston unit having an engine cylinder, and a free-piston therein, a compressor cylinder and piston, the compressor piston being connected to and moving with the engine piston, said compressor cylinder including a cylinder head with valves therein, and a cylindrical wall,

said wall being axially movable with respect to said head and having at leastone port therein, and means for moving said cylindrical wall axially with respect to the cylinder head to adjust the position of said port with respect to said head.

3. In a free-piston unit having an engine cylinder, and a free-piston therein, a compressor cylinder and piston. the compressor piston being connected to and moving with the engine piston, said compressor cylinder including a cylinder head with discharge valves therein, and a cylindrical outer wall, said wall having a sliding connection with said head and being axially movable with respect to said head, said wall having a numher of slots therethrough, the ends of the slots adjacent to said head being normally spaced from the head, in combination with'means for moving said outer wall axially with respect to the head to adjust the spacing between the ends or the slot and the head.

4. In a free-piston unit having an engine cylinder, and a free-piston therein, a compressor cylinder and piston, the compressor piston being connected to and moving with the engine piston, said compressor cylinder including a cylinder head with discharge valves therein, and a cylin-f drical outer wall, said wal1 having a sliding connection with said head and being axially movable with respect to said head, said wall having a number of slots therethrough, the ends of the slots adjacent to said head being normally spaced from the head, in combination with means for moving said outer wall axially with respect to the head to adjust the spacing between the ends of the slot and the head, and means for guiding said outer wall at the end remote from the cylinder head.

5. In afree-piston unit having an engine cylinder, opposed free-pistons therein, compressor cylinders at opposite ends of the engine cylinder, a compressor piston in each compressor cylinder, each compressor being connected to and movable with the adjacent engine piston, each compressor cylinder having a cylinder head with valves therein, and an outer wall for each compressor cylinder with at least one port therein, means for guiding each of said outer walls for axial movement with respect to the associated cylinder head, and means for moving both of said outer walls simultaneously toward or away from the center of the engine for changing the position of the ports relative to the normal piston stroke.

6. In a free-piston unit having an engine cylinder, opposed free-pistons therein, compressor cylinders at opposite ends of the engine cylinder, a compressor piston in each compressor cylinder, each compressor being connected to and movable with the adjacent engine piston, each compressor cylinder having a cylinder head with valves therein, and an outer wall for each compressor cylinder with at least one port therein, said wall being axially movable relative to the cylinder head and means for moving both of said outer walls simultaneously toward or away from the center of the unit for changing the spacing between the ports and the cylinder heads.

7. In a free-piston unit having an engine cylinder, opposed free-pistons therein, compressor cylinders at opposite ends of the engine cylinder, a compressor piston in each compressor cylinder, each compressor being connected to and movable with the adjacent engine piston, each compressor cylinder having a cylinder head with valves therein, and an outer wall for each compressor cylinder with at least one port therein, each of said outer walls being guided for axial movement with respect to the associated cylinder head, means for moving said outer walls simultaneously toward or away from the center of the unit, and means for guiding the end of each cylinder wall remote from the cylinder head.

WALTER A. LEDWITH.

REFERENCES CITED The following references are of record in the file of this patent:

(References on following page) Number UNITED STATES PATENTS Name Date Merritt June 23, 1896 Doelling Jan, 28, 1908 Spardo Jan. 27, 1914 Dwyer Jan. 22, 1924 Riesner Apr, 6, 1926 Janicke July 6, 1937 Number 5 39,764

Janicke Dec, 22, 1936 FOREIGN PATENTS Country Date France Nov, 24, 1931 (Addition to No. 698,563) Germany 1903 Great; Britain May 15, 1930 Great Britain July 23, 1925 

